I used Trim Fix High Temp. It is an aerosol, but was what Martrim recommended. Mess wise, it's fairly controllable, I did use 2 wallpaper pasting tables covered in some old curtains to catch the over spray. Your point about gaps could be valid, by and large it's not been a problem, but the bits where you have to stretch the material i.e. round the horn, in the grab handle resess has come unstuck, I don't think it is through a lack of glue (used 2 cans), more about the strength of the glue, thankfully it doesn't look too bad as it's hidden by the handles and the bit around the horn is the same both sides, the rest of the headliner has gone on really well and held up to the insane temps we've had.
I used this YouTube vid to get a good idea of how to approach it.